ETF (electron transfer flavoprotein) is a heterodimer of an alpha and beta subunit. The ETFB protein is electron-transfer-flavoprotein, beta polypeptide, which shuttles electrons between primary flavoprotein dehydrogenases involved in mitochondrial fatty acid and amino acid catabolism and the membrane-bound electron transfer flavoprotein ubiquinone oxidoreductase. Recombinant human ETFB protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography.